Method of dispersing iron

ABSTRACT

A method of comprising iron in an aqueous system comprising adding to the system a copolymer of styrene sulfonic acid and methacrylic acid or its water soluble salt in an amount effective to disperse the iron contained therein.

FIELD OF THE INVENTION

The invention relates to an improved method for dispersing iron inaqueous systems, and more specifically, it relates to the use of thecopolymers of styrene sulfonic acid and methacrylic acid or their watersoluble salts for dispersing iron in aqueous system.

BACKGROUND OF THE INVENTION

The control of iron precipitation in the presence of dissolve calcium isimportant in aqueous pigment dispersions, color strength improvement,ore flotation, manufacture of pulp and paper, slurry viscosityreduction, metal treating operations, textile processing, and watertreatment.

While organophosphonates (e.g. amino tri(methylphosphonic acid) andhydroxyethylidene diphosphonic acid) and polyphosphates (e.g. sodiumtripolyphosphate and sodium hexametaphosphate) have been used to inhibitthe precipitation of iron, the organophosphonates are unfortunatelysensitive to calcium hardness and prone to form calcium phosphonateprecipitates. Polyphosphates are not thermally stable and will hydrolyzein an aqueous system to form orthophosphate which is extremely sensitiveto calcium.

For these reasons, the use of the organophosphonates and polyphosphatesheretofore in controlling iron precipitation have not been completelysatisfactory. We have now discovered that copolymers of sodium styrenesulfonate and methacrylic acid are highly active iron dispersants. Thecopolymers of this invention are insensitive to calcium hardness and arethermally stable.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a method for dispersingiron in aqueous systems.

It is another object of this invention to provide a novel irondispersing agent which are insensitive to calcium hardness.

It is another object of this invention to provide a novel irondispersing agent which are thermally stable.

In accordance with the present invention there has been provided amethod for dispersing iron particles in aqueous systems which comprisesadding to the system, in an amount effective to disperse the ironparticles, a copolymer of sodium styrene sulfonate and methacrylic acid.

DETAILED DESCRIPTION

The present invention is directed to the use of certain copolymers ofsodium styrene sulfonate and methacrylic acid as an iron dispersingagent for treating aqueous systems. More specifically, the method ofthis invention comprises adding a copolymer of sodium styrene sulfonateand methacrylic acid, or water soluble salts thereof, to an aqueoussystem in an amount effective to disperse iron particles containedtherein.

The copolymers of the present invention, in general, have a mole ratioof sodium styrene sulfonate: methacrylic acid in the range of 5:95 to95:5, respectively, preferably in the range of 10:90 to 90:10respectively, and most preferably in the range of 20:80 to 80:20respectively. Suitable copolymers for use in this invention havemolecular weights of at least 600, preferably greater than 2,000 and aregenerally less than 1,000,000, preferably less than 100,000.

Calcium insensitivity is considered an important feature of thisinvention because it allows the copolymer of this invention to be usedeffectively in water of relatively high hardness. A calcium sensitivitytest was devised to determine the tendency of a chemical to precipitatewith calcium ions in solution. The test for calcium insensitivity of acompound, as used in this application, involves a cloud point test wherethe compound is added to a hard water containing 500 ppm calcium ion (asCaCO₃) which is buffered at pH 8.3 using 0.005 M borate buffer and has atemperature of 60° C. The amount of compound which can be added untilthe solution becomes turbid (the cloud point) is considered to be anindicator of calcium sensitivity. This cloud point test will be referredto herein as the "CA500 cloud point test". The calcium insensitivecompounds of this invention have cloud points of at least about 25 ppmas determined by the CA500 cloud point test. Preferred compounds have acloud point of a least 50 ppm; and the most preferred compounds have acloud point of at least about 75 ppm as determined by the CA500 cloudpoint test because they are considered particularly versatile withregard to the water systems in which they can be effectively used.

As is apparent from the results illustrated in Table 1, not allphosphonates or polyphosphates have suitable CA500 cloud points. Forexample, calcium phosphonate precipitates formed with aminotri(methylphosphonic acid) and hydroxyethylidene diphosphonic acid withcloud points of 10 ppm and 7 ppm, respectively. These results indicatethat amino tri(methylphosphonic acid) and hydroxyethylidene diphosphonicacid are very sensitive to calcium hardness and prone to form calciumphosphonate precipitates at low treatment concentrations. Calciumphosphate precipitates form with orthophosphate (e.g. monosodiumphosphate) with a cloud point <3 ppm indicating that the orthophosphateis extremely sensitive to calcium. On the contrary, the copolymers ofthe instant invention, as illustrated in Table 1, were relativelyinsensitive to calcium.

                  TABLE 1                                                         ______________________________________                                                            Comonomer    Cloud                                                            Ratio by     Point                                        Additive            Mole         ppm                                          ______________________________________                                        Amino tri(methylphosphonic acid)                                                                  --             10                                         Hydroxyethylidene diphosphonic acid                                                               --             7                                          Sodium tripolyphosphate                                                                           --             20                                         Monosodium phosphate                                                                              --            <3                                          Sodium styrene sulfonate -                                                                        25:75        >100                                         methacrylic acid copolymer                                                    (Sample No. 1052-95A)                                                         Sodium styrene sulfonate -                                                                        20:80        >100                                         methacrylic acid copolymer                                                    (Sample No. 1077-67C)                                                         Sodium styrene sulfonate -                                                                        16.2:83.8    >100                                         methacrylic acid copolymer                                                    (Sample No. 1052-95B)                                                         Sodium styrene sulfonate -                                                                        15:85        >100                                         methacrylic acid copolymer                                                    (Sample No. 1077-71D)                                                         Sodium styrene sulfonate -                                                                        10:90          57                                         methacrylic acid copolymer                                                    (Sample No. 1077-65C)                                                         ______________________________________                                    

Another important feature of this invention is the thermal stability ofthe copolymers of the invention. A thermal stability test was devised tomeasure the stability of a chemical at elevated temperatures andpressures.

The thermal stability of several water treatment compounds including thecopolymers of this invention were tested at 279° C. and 900 psig inwater. The results after heating for 4 hours and 21 hours areillustrated in Table 2.

                  TABLE 2                                                         ______________________________________                                                           % Recovery                                                 Additive             4 Hours  21 Hours                                        ______________________________________                                        Amino tri(methylphosphonic acid)                                                                   59.6     33.5                                            Hydroxyethylidene diphosphonic acid                                                                53.9      2.7                                            Sodium tripolyphosphate                                                                            0        --                                              Sodium hexametaphosphate                                                                           0        --                                              Sodium styrene sulfonate -                                                                         86.7     77.5                                            methacrylic acid copolymer 25:75                                              (Sample No. 1052-95A)                                                         Sodium styrene sulfonate -                                                                         83.2     79.0                                            methacrylic acid copolymer 20:80                                              (Sample No. 1077-67A)                                                         Sodium styrene sulfonate -                                                                         97.7     77.8                                            methacrylic acid copolymer 15:85                                              (Sample No 1077-66C)                                                          Sodium styrene sulfonate -                                                                         85.3     71.8                                            methacrylic acid copolymer 5:95                                               (Sample No. 1052-85C                                                          Sodium polymethacrylate                                                                            74.6     50.4                                            ______________________________________                                    

The iron dispersing agents of the present invention may be used invarious aqueous systems including, but not limited to, cooling watersystems, desalinization units, gas scrubbers, boiler systems,recirculating water systems and the like. Due to the thermal stabilityand calcium insensitivities of the copolymers of this invention, theclaimed iron dispersing agents are most advantageously used in systemshaving high hardness and/or high temperature and pressure conditionssuch as, e.g., steam generating boilers.

In accordance with this invention, iron particles may be effectivelydispersed in aqueous systems by adding to the system an effective amountof a copolymer of sodium styrene sulfonate and methacrylic acid. Theprecise dosage amount of the iron dispersing agents of this inventiondepends, to some extent, on the nature of the aqueous system in which itis to be incorporated and the degree of protection desired, as well asthe amount of iron particles which may be present in the system. Ingeneral, however, the concentration of copolymer maintained in thesystem water can be from about 0.1 ppm to about 10,000 ppm. Within thisrange, generally low dosages of about 1 ppm to 500 ppm are preferred.Thus, the exact dosage amount is not per se critical to the invention,and those skilled in the art can readily determine the appropriatedosage by conventional means.

The iron dispersing agents of this invention may be added to the aqueoussystem by any convenient mode, such as by first forming a concentratedsolution, preferably with water and containing between 1 and 50 totalweight percent of the copolymer, and then feeding the concentratedsolution into the aqueous system at some convenient point. In manyinstances the iron dispersants may be added to the make-up or feed waterlines through which water enters the system.

The iron dispersants of the instant invention may also be usedadvantageously with other known water treatment agents including, butnot limited to scale inhibitors, corrosion inhibitors, phosphates,phosphonates, yellow metal corrosion inhibitors, pH regulators, otherdispersants, oxygen scavengers, and the like as mixtures thereof.

The following examples are provided to illustrate the present inventionin accordance with the principles of this invention, but are not to beconstrued as limiting the invention in any way except as indicated inthe appended claims. All parts and percentages are by weight unlessotherwise indicated.

EXAMPLE 1

The effectiveness of sodium styrene sulfonate-methacrylic acid copolymer(Sample No. 1052-95A) was tested for dispersing iron oxide powder. Theiron oxide is a reagent grade ferric oxide powder supplied by J. T.Baker, Inc. It contains ferric oxide (Fe₂ O₃) 99.7%, phosphate (PO₄)0.01%, sulfate (SO₄) 0.05%, copper (Cu) 0.001%, manganese (Mn) 0.02%,and zinc (Zn) 0.001%.

To a 25 mm diameter round cell containing a small 13 mm long magneticstirring bar is added 30 ml of ferric oxide suspension (0.1% in Chicagotap water). Treatment is added to this suspension and the contents aremixed for one minute. Now the cell is removed from the magnetic stirrerand the light transmittance vs. time is measured after standing for 0.5hour, 1 hour and 2 hours, using a Coleman spectrophotometer at thewavelength of 450 nanometers.

    ______________________________________                                        Concentration of Sodium                                                                         % Light Transmittance                                       Styrene Sulfonate-                                                                              after Standing for:                                         Methacrylic Acid Copolymer                                                                      0.5 Hour 1 Hour   2 Hours                                   ______________________________________                                        0 ppm             17.4     53.0     62.4                                      2 ppm             1.4      10.6     31.3                                      6 ppm             0.7      5.5      22.8                                      8 ppm             0.9      7.3      17.5                                      10 ppm            0.7      4.3      18.4                                      ______________________________________                                    

As shown in the above table, the sodium styrene sulfonate-methacrylicacid copolymer is very effective in dispersing ferric oxide powder.

EXAMPLE 2

Sodium styrene sulfonate-methacrylic acid copolymer was further testedfor it stability to disperse hematite. The copolymers were dissolved at2.5 ppm in Chicago tap water, and the pH was adjusted to 8.0±0.2.Anhydrous hematite (Fe₂ O₃, 1-5 micron particles size, 0.1%) was added,and the mixtures were shaken at 300 rpm for 17 hours at 54° C. Themixtures were than allowed to settle for 30 minutes, and samples werewithdrawn at 50% depth and analyzed for total iron by atomic absorptionspectrometry.

    ______________________________________                                        Additive          % Hematite Dispersed                                        ______________________________________                                        Blank             3.5                                                         Sodium styrene sulfonate -                                                                      87.0                                                        methacrylic acid copolymer                                                    25:75 (Sample No. 1052-95A)                                                   Sodium styrene sulfonate -                                                                      63.0                                                        methacrylic acid copolymer                                                    15:85 (Sample No. 1052-95B)                                                   Sodium styrene sulfonate -                                                                      40.0                                                        methacrylic acid copolymer                                                    5:95 (Sample No. 1052-95C)                                                    ______________________________________                                    

It can be seen that the sodium styrene sulfonate-methacrylic acidcopolymer is very effective in inhibiting the precipitation of hematiteparticles in aqueous system.

EXAMPLE 3

The effectiveness of sodium styrene sulfonate-methacrylic acid copolymer(Sample No. 1052-95A) was tested for dispersing rust formed from couponcorrosion. The rust formed from coupon corrosion is collected from thebottom of the beaker, where suspended mild steel coupons had beenexposed to a salty atmosphere by bubbling a brine solution. The rust wasfiltered, washed with water and air-dried before use.

To a 25 mm diameter round cell containing a small 13 mm long magneticstirring bar is added 30 ml of rust suspension (0.1% rust in Chicago tapwater). Treatment is added to this suspension and the contents are mixedfor one minute. After mixing, the cell is removed from the magneticstirrer and the light transmittance vs. time is measured after standingfor 0.5 hour, 1 hour, 2 hours and 3.5 hours, using a Colemanspectrophotometer at the wavelength of 450 nanometers.

    ______________________________________                                                          % Light Transmittance                                       Concentration of Sodium                                                                         after Standing for:                                         Styrene Sulfonate-                                                                              0.5    1       2     3.5                                    Methacrylic Acid Copolymer                                                                      Hour   Hour    Hours Hours                                  ______________________________________                                        0 ppm             11.2   27.8    48.8  58.3                                   2 ppm             1.0    1.3     2.9   20.0                                   4 ppm             1.0    1.2     2.4   17.7                                   6 ppm             1.2    1.4     2.8   20.8                                   8 ppm             1.0    1.3     2.4   18.4                                   10 ppm            1.0    1.4     2.2   13.0                                   ______________________________________                                    

It is evident from the above table that the sodium styrenesulfonate-methacrylic acid copolymer is highly effective in dispersingiron oxide from rusted coupons.

EXAMPLE 4

A test water containing 5 ppm ferric chloride (as Fe), 5 ppm polymer, 30ppm calcium (as CaCO₃), 10 ppm magnesium (as CaCO₃), 4 ppm silica and 45ppm bicarbonate (as HCO₃) was prepared. The polymer under test was addedto water after the addition of the ferric chloride but prior to theaddition of calcium, magnesium, silica or bicarbonate. The pH of thesolution was raised to pH 11.0, which precipitated the soluble ferricchloride in situ as ferric hydroxide. The resultant mixture was refluxedfor 3 hours. The hot solution (250 ml) was decanted into a 250 mlgraduated measuring cylinder and allowed to settle for 23 hours. At theend of the test a small sample of test water was removed from the top ofthe liquid and the concentration of iron determined.

A good iron dispersant will maintain most of the iron suspended insolution at the end of the test, hence giving an iron concentrationclose to the initial value of 5 ppm.

Experimental results of the settlement test are shown below.

    ______________________________________                                                            Concentration of Iron                                                         in Test Water after                                       Additive            23-Hour Settling, ppm                                     ______________________________________                                        Blank               0.63                                                      Sodium styrene sulfonate -                                                                        4.88                                                      Methacrylic Acid Copolymer                                                    25:75 (Sample No. 1052-95A)                                                   Sodium styrene sulfonate -                                                                        4.76                                                      Methacrylic Acid Copolymer                                                    20:80 (Sample No. 1077-67C)                                                   Sodium styrene sulfonate -                                                                        4.64                                                      Methacrylic Acid Copolymer                                                    17.4:82.6 (Sample No. 1052-91B)                                               Sodium styrene sulfonate -                                                                        4.76                                                      Methacrylic Acid Copolymer                                                    16.2:83.8 (Sample No. 1052-95B)                                               Sodium styrene sulfonate -                                                                        4.69                                                      Methacrylic Acid Copolymer                                                    15:85 (Sample No. 1077-66C)                                                   Sodium styrene sulfonate -                                                                        4.71                                                      Methacrylic Acid Copolymer                                                    10:90 (Sample No. 1007-65A)                                                   Sodium styrene sulfonate -                                                                        4.64                                                      Methacrylic Acid Copolymer                                                    5:95 (Sample No. 1052-85C)                                                    ______________________________________                                    

As shown in the above table, the sodium styrene sulfonate-methacrylicacid copolymer is highly effective in preventing the settling of ferrichydroxide.

We claim:
 1. A method of dispersing iron in an aqueous system comprisingadding to the system a copolymer of styrene sulfonic acid andmethacrylic acid or its water soluble salt in an amount effective todisperse the iron contained therein wherein said copolymer has a molarratio of styrene sulfonic acid: methacrylic acid from 5:95 to 95:5. 2.The method of claim 1 wherein the molar ratio of styrene sulfonicacid:methacrylic acid is from 10:90 to 90:10.
 3. The method of claim 1wherein the molar ratio of styrene sulfonic acid:methacrylic acid isfrom 20:80 to 80:20.
 4. The method of claim 1 wherein the molecularweight of the copolymer ranges from 600 to 1,000,000.
 5. The method ofclaim 1 wherein the molecular weight of the copolymer ranges from 2,000to 100,000.
 6. The method of claim 1 wherein the water soluble salt is asodium salt.